Our Hemlocks Are Endangered
By Don Gasper
We might be aware of the Balsam Wooly Adelgid that has ravaged our rare high elevation Balsam Fir. Another evergreen, the Hemlock, is similarly endangered. There is also a Hemlock Wooly Adelgid in West Virginia. It has spread from Virginia in the 1950's to the Northeast and now into The Smokies. Ladybugs from the Adelgid’s homeland in Asia are being released to control it in nearly a dozen eastern states. If left unchecked in the next 50 years our majestic Hemlock will be only a memory. The Adelgid infestation year-round looks like a white cottony mass at the base of the needles. The needles are gray-green and thinned having dropped prematurely. It spreads about 15 miles a year. It is spread by wind, birds, and mammals.
We know our beloved Hemlock well. Moist sites are favorites of the Hemlock where they can grow up to 100' tall and 5' in diameter. They particularly border streams, and the Adelgid seems particularly destructive of streamside beauty and shade. Groups grow in draws that create a dark cooler, almost cathedral-like atmosphere. (The big trees in Cathedral State Park are Hemlock.) It is quieter, unless the wind is blowing, or the marvelous song of the Hermit or Wood Thrush is uniquely heard. Other birds, too, forage, shelter, and nest in them. Their needle substrate contributes to a forest floor that nourishes characteristic plants and animals – salamanders, millipedes, shrews, voles, mice, chipmunks, flying squirrels, and the eastern red squirrel. Hemlock groves form their own unique microhabitat and are a critical component of larger ecosystems. The Hemlock extends throughout Appalachia. Its common presence characterizes our mountains. It is a dominant climax big tree that may live 800 years. All are aware of its values. It grows in some of our yards. It is important commercially (with 274 cultivar ornamental varieties). It is used for timber.
The Adelgid sucks sap from needle bases. In 1990 90% of the Hemlocks in Shenandoah National Park were healthy, now only 5% are. In only 5 years sometimes a huge tree will die. It will stand as a gray skeleton for 20 years. Size and age makes no difference. Like aphids, Adelgids reproduce without a sexual union twice a summer so their numbers increase rapidly.
It will take years for the introductions of this ladybug to build to control the Adelgid. This ladybug eats only this Adelgid, starving to death otherwise. Some releases have been shown to reduce the Adelgid population almost 90% - with no other effects. Let us hope, and be sure that everything is being done that can be done to preserve this beloved tree.